[GorgeRonde]

Listening to what ? To the dude that tells me that's not possible and proceeds to dump a big pile of authority on top of my head or to my own experiment that tells me another story ?

I would have preferred to be told:

- yes and no. You'll get warnings if you try to return a pointer to a local, however, doing this and that, you can manage to do it.

- but once you have achieved that, the result will be dependent on the way the stack is handled (not really in your control). You'll feel some comfort doing this in recursive calls, however beware of signal.h.

But this isn't the answer I received. I guess C programmers do not know the difference between what you can do (however risky) and what you shouldn't do. Also when someone asks such "weird" questions, do not assume he's a beginner with no notion of what constructs he can handle safely, maybe he's someone trying to find the limits of C – and once these limits are identified it can be a good conversation starter about C's internal and the way various compilers differ.

Edit: also downvotes on HN are not like downvotes on Reddit: there's actually a limit (-2 ?). Below this the comment disappears. Conclusion: only downvote when the comment engages in antisocial behavior (not respecting the rules or common human decency, etc ...), not when you disagree with it. I always upvote an unfairly downvoted comment for these reasons.

[dahart]

I was trying to help by explaining it, instead of saying go read K&R, but I don’t get the feeling you really heard or understood me. There is no other story. There is no yes and no. There is only no. You cannot manage to do it. It does not work to return local memory from a function, ever, period. Once you return, it is 100% unsafe to try to use the memory from your previous stack. There is absolute zero comfort in recursive calls.

You are mistaking some luck in having it not crash once for thinking that it’s okay in some situations. It’s not okay under any circumstances. That’s what makes this even more dangerous. Your program could crash at any time. It might run a thousand times and then suddenly start crashing. It might always run for you, and then crash on other people. But just because it runs once without crashing doesn’t mean it’s working.

A signal is not the only way your function’s stack can get stomped on the very next instruction after you return. Other processes and other threads can do it, the memory system can relocate your program or another one into your previous memory space. Recursive calls are guaranteed to stomp on previous stack frames when your recursion depth decreases and then increases, the previous stack will be overwritten.

Returning a pointer to a local stack frame is always incorrect. It’s not risky, it’s wrong.

BTW: you have the ability to see comments below the downvote limit, go to your profile settings and turn on showdead.

I didn’t downvote you, if that’s why you were trying to explain voting behavior to me, but you will find on HN that downvotes and upvotes both happen for a wide variety of reasons, and are not limited to either whether people agree, nor whether the comments are polite. Downvotes are often cast for comments that break site guidelines, for example just failing to assume good faith can get you downvoted. So can making blanket generalizations about a group of people, like the above “I guess C programmers do not know the difference...”. See the comments section here: https://news.ycombinator.com/newsguidelines.html

I sometimes upvote what appear to be unfairly downvoted comments to me. I usually upvote people who read and respond to me, regardless of whether I agree with them.

[GorgeRonde]

    - Java: no
    - Ruby: no
    - PHP:  no
    - C:    yes and no

[dahart]

?? I don’t understand what you mean. Those other languages don’t have pointers, they only have references, but what do they have to do with this?

Why do you still think there’s some yes in C? It’s not making sense yet that your memory is gone after you return? Returning a pointer to a local variable is exactly the same as calling delete or free on a pointer and then reading from it. You officially don’t own the memory after a return statement, so if you try to use it, then what happens is indeterminate. Again, since it doesn’t seem to be sinking in: it is always wrong to return a pointer to local memory. But, if you really really don’t want to listen, and you’re sure it works sometimes, then I say go for it!